Electrical contacts and terminals have long been used to terminate and connect a variety of pins which carry electrical power or signals. A number of electrical terminal configurations are known and used in the art, including sockets, spring-like tines and flexible spring-arms. The present invention is directed to electrical terminals of a "tuning fork" configuration, which are generally known in the art.
Certain tuning fork configurations have been developed for use in various connector structures. In applications subject to high vibration or shock forces, a terminal with high retention forces is required to prevent detachment of a mating contact during operation. The tuning fork design is advantageous because the outward deflection of a pair of retention beams upon insertion of a mating pin contact creates a good contact force between the terminal and the inserted contact pin. However, electrical terminals of the tuning fork type configuration are not without certain disadvantages. A male contact pin which is retained by the fork design may have rough connection surfaces due to shearing during die stamping of the pin. The contact faces of the two retention beams of the tuning fork terminal likewise are sheared edges of material produced during a stamping operation and therefore have a comparatively rough surface finish. The interface between these rough surfaces creates a poor electrical contact between the pin and the terminal and an increased possibility of damage to the terminal and the contact during repeated mating cycles.
There have been numerous attempts to overcome the problems inherent in conventional tuning fork designs. For example, a terminal shown in U.S. Pat. No. 4,140,361 has a receptacle having a pair of opposing cantilever legs with a resilient cantilever leg centered therebetween. The center leg makes connection with one side of a mating pin while the other two legs contact the other side of the mating pin. The two opposing legs will deflect outwardly upon insertion of a pin therebetween, thus assuring satisfactory contact forces are being applied so as retain such pin. The opposing legs and the center leg are offset from a cable engaging portion, significantly adding to the space occupied by the terminal. None of the legs which receive a mating pin is coated with a conductive material which would facilitate electrical connection between the terminal and the pin.
A similar prior art design is shown in U.S. Pat. No. 4,598,972. This type of terminal is referred to as a "clip-on lead". A clip-on lead has an elongated shaft suitable for electrical connection, the upper end of which widens into a pair of fork-like bracing members. A front spring member protrudes normal to the bracing members and curves into a plane which is parallel to that of the bracing members. Both the rear bracing members and the front spring member are soldered to a substrate received therebetween. As a result, the lead is much harder to separate from the substrate, a characteristic that is highly desirable in high shock/high vibration environments. However, the protrusion of the elongated shaft from a rear surface of the substrate significantly increases the electrical length from the substrate to a PC board, adversely affecting the performance of a high frequency circuit.
A problem inherent in the above described configurations is that the high normal force exerted by the beams can also damage the contact area, leading to premature failure of the connector system. Additionally, if the contact surfaces of the forks are plated or otherwise covered in a conductive material such as gold, the combination of high retention forces and rough material edges causes damage to the covering, resulting in lower operational life and correspondingly higher production and maintenance costs.
An alternative tuning fork terminal configuration is disclosed in U.S. Pat. No. 5,252,097. This patent provides for a female electrical terminal having a pair of flexible beams constituting a contact member and extending in a plane which is substantially perpendicular to the flexible beams. The contacting surfaces of each flexible beam has a coating layer of gold or tin. The deflection of the contact beams in this configuration is predetermined before assembly, thereby enabling high contact precision after assembly. The deflection of the flexible beams is limited by the guiding beam and is independent of the introduction of a conventional male pin contact. In use, the high and constant contact pressure protects against corrosion of the contact areas and provides integrity of a transmitted signal in cases of vibration or impact. However, this connector, like the other connector designs, makes it very difficult to deposit gold selectively onto the contact area. This means the entire ends of the beams must be immersion plated, a process which results in high gold consumption and correspondingly high manufacturing costs.
Therefore, it is desirable to provide an electrical terminal that provides a high retention force without reducing the operating life of the terminal.